Process for manufacturing steel plates.



P. GIOLITTI.

PROCESS FOR MANUFACTURING, STEEL PLATES.

APPLICATION FILED SEPT. 6, 1906.

Patented Apr. 30, 1912.

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FEDERICO GIOLITTI, OF ROME, ITALY, ASSIGNOR TO SOCIETA .ANONIMA ITALIANA GIO. ANSALDQ ARMSTRONG & CO, 01 GENOA, ITALY, A CORPORATION OF ITALY.

PROCESS FOR MANUFACTURING STEEL PLATES.

To all whom it may concern: I

Be it known that I, FEoERroo GIOLITTI, doctor of chemistry, a subject of the King of Italy, and a resident of Rome, Italy, have Y the proportion of carbon contained but also as regards the presence in some of them of foreign metals and as regards the proportions in which these metals enter into the composition. This latter varies gradually in passing from one zone to another.

The accompanying drawing illustrates diagrammatically a steel plate after treatment according to the present invention.

The result in question is obtained by sub mitting the mass of homogeneous steel (either ordinary carbon steel or a special ternary, quaternary or like steel) to the action of suitable granular mixtures containing the metal it is desired to-introduce into the steel, such as principally chromium, nickel, tungsten, molybdenum, vanadium and sometimes silicon anduranium in a free state or in a state of readily disassociated combination, which as is hereinafterstated varies from one preparation to the other as well as from one phase to the other of the same preparation. These granular mixtures ought to be strongly compressed against one or both surfaces of the plate or other article to be treated.

For each given composition of the homogeneous steel which forms the mass under manipulation as well asfor one or more of the given metals contained in the mixture employed, there exists a determined interval or range of temperature, which depends strictly on the position of the critical inter vals of the homogeneous steel itself and on the nature of the metals employed. It is in this interval that takes place the difiusion of the metal or metals contained in the mixture compressed against the surfaces of the mass of steel toward the interior of this mass itself. The interval'of temperature referredto above which is the most suitable for obtaining the diffusion in question, is comprised between the temperature of the Specification of Letterslatent.

Application filed September 6, 1906.

Patented Apr. 30, 1912.

Serial No. 333,408.

highest critical point of the steel employed and a temperaturenear its point of fusion.

The depth to which the metal contained in the granular mixture extends into the homogeneous mass of steel submitted to such an operation depends above all on the length of the operation; but even by considerably prolonging this duration a very deep or gradual diffusion would not be obtained in the greater number of cases if the tempera ture were always maintained constant from the beginning of the operation until the end. In the drawing, representing the bar of treated material, the face a represents the bar unaltered while the other face bindicates the zone of treatment that extends into the middle and is graduated in. composition.

The constancy of the temperature--21 con- .dition which would be very useful if a certain concentration as regards the foreign metal introduced had not-been surpassed and y if a greathomogeneousness of concentrating for a given zone of the plate had to be obtainedprevents a very definite given limit of concentration being surpassed, because if this latter is increased there is produced a displacement of the critical intervals and consequently of the interval of temperature in which the diffusion can be-etfected. It results that at a certain moment the temperature maintained constant is no longer comprised in this interval and consequently the passage of the metal of the mixture to the mass under treatment is no longer effectedand the diffusion is effected only at the interior of the mass until the concentration is suitably lowered owing to the interior diffusion referred to. It will then generally be advisable to suitably alternate the reduction and the increases of temperature in limits which can easily be determined for each case and which generally ought to determine the beginning and the ending of the critical intervals.

The product of the treatment referred to above will consistofa heterogeneous mass of steel, the composition of which varies in the various zones or layers according to the composition of the micro'construction of the homogeneous steel started with, the composition of the granular mixture employed and the fixed or variable conditions of temperature in which the operation is effected.

if a granular mass containing only one metal is used for the treatment and compressed against only one face of the ingot, the result will be (beginning with the sufface which has been submitted to the operation) a block formed of a ternary steel in which the proportion of the characteristic metal decreases toward the interior of the block until at a certain depth this temper is reduced to zero. From this moment the ingot will still be formed of the same primitive carbon steel which ma 1 have (as well as the ternary zone) the same initial proportion of carbon ora difierent proportion acexample,

. employing a mixture of cording as the granular mass did not contain active substances or was more or less rich in carbon or metallic oxid. As example a steel carbon plate (0.1 to, 0.2 per cent. of carbon) tact with a mixture of wolframic acid or of substances suitably carbonaceous or nitrogenous compressed against. one of its surfaces at a temperature near that of fusion. As an example of such nitrogenous substances may be mentioned: charcoal 50%, bone-black 20%, carbonate of barium 25% and ferrocyanid of potassium 5%. In this case the vprecedingoperation must be followed by a superficial decarbonization obtained by means of heating in contact with the mixtures of ordinary metallic oxids. On. the contrary if a start is made with a .ternary homogeneous steel ingot (for a chrome steel with 2 to t per cent. of chrome) the final product would have a similar structure to that of the preceding ingot but the layer of ternary steel would be substituted by a layer of quaternary steel,

while the rest of the mass would still be ternary steel. I In the case just mentioned by the preceding case the quaternary layer will consist of chrome steel and Wolfram steel. The procedure is followed in a similar manner for the more complex steels. Simliar considerations will apply in the case where the treatment by diffusion is effected on two surfaces or on all the surface of the steel objects, in one, two or more times, these operations alternating with thermic treatment (temperings and the like) or suitable mechanical operations which may vary for each case according to the nature of the steel started with and of the steel obtained.

The operation above referred to may be applied directly to the mass of homogeneous steel as cast, or to the mass already brought to the desired shape by the ordinary mechanical manipulations, I (hammering, "rolling, pressing and the like).

however, it would almost always be necessary to follow the chemical treatment described above by a suitable thermic treatment. But it is in the temper of the metallic pieces where the greatest advantages hardness, plasticity,

may be taken, maintained in conascertained the nature of my In every casz, I

of this method of manufacture and the suglven composition for the various zones of the piece of steel can be obtained and consequently the various parts of the object may be given the most suitable composition to be obtained whereby through a homogeneous tempering .and applied to the whole, each part acquires the physical, chemical or mechanical properties (such as magnetic properties, resistance to chemical agents, elasticity and the like) the most suitable for the purposes for which the piece hasto be utilized. By this method armor plates for example, can be obtained which after one or more homogeneous and total temperings effected under the desired conditions of temperature and'the like, possesses' mechanical properties (hardness, tenacity, and the like) differing. in their various layers so that they can adapted to the most varied uses;

Let us, srppose for example to have to treat a special nickel steel showing the followingcomposition: nickel 2.20%; carbon 0.10%, manganese 0.42%, silicon 0.30%, sulfur 0.04%, phosphorus 0.02%, and that it-be intended to obtain a Zone of 3 mm. thickness, in which the percentage of carbon should vary from 0.9% (on therouter face) down to 0.4% at 3 mm. depth, while. the percentage of manganese, namely of the metal to be introduced by diffusion accord ing to the present invention, should vary between 3% (on the outer face) and 0.7% at 3 mm. depth. In order to obtain this result it will be suflicient to heatthe steel piece in contact with a granular mixture consisting of three parts of charcoal, one of finely pulverized manganese dioxid and one of barium carbonate. 1150 degrees C. is to be kept up during about half of an hour; whereupon the same is to be allowed to gradually drop down to 700 degrees C. at the end of the three hours.

'In making these statements, as to the dura tion of the heating, it has been assumed that the time begins to run since the full heat has been laid on the steel pieces; the addi tional time necessary for reaching the aforesaid temperaturcs as well as for cooling after. each treatment, the size of the pieces and the arrangement of the heating furnaces.

aving now particularly described and said invention and in what manner the same is to be performed, I declare that what I claim is 1. The process of forming steel. plates or other articles, consisting in subjecting one or more surfaces of the article to contact with a certain characteristic metal steel be most suitably.

A temperature of of course depends-upon,

component, and at the same time to a material capableof varying the proportion of other articles, consisting in subjecting one or more surfaces of the article to contact with a certain characteristic metal steel component and to a suitable decarbonizing material for a considerable period of time and at a temperature 'sufiicient by itself to cause diffusion -into the article for a considerable distance to form a zone in the article in which the percentage of the component metal united with the steel is graded from a maximum inwardly to a minimum and in which the proportion of carbon in the said zone is less than the original quantity. r

3. The process of forming steel plates or other articles consisting in subjecting one or more surfaces of the article to contact with a certain characteristic metallic steel component, fora considerable period of time and at a temperature between that of the I highest critical point of the steel employed and a temperature near its point of fusion whereby to cause diffusion into the article for a considerable distance to form a zone in the article in which the percentage of the component metal united with the steel is graded from a maximum inwardly to a minimum.

4. The process of forming steel plates or other articles consisting in subjecting one or more surfaces of the article to contact with a certain characteristic metal steel component, and at the same time to a material capable of varying. the proportion of carbon in the article, for a considerable period of time and at a temperature between that of the highest critical point of the steel emloyed and a temperature near its point of usion whereby to cause diflusion into the article for a considerable distance to form a zone in the article in which the percentage of the component metal united with the steel is graded from a maximum to a minimum and 1n which zone the proportlon of FEDERIOO GIOLITTI.

Witnesses Gr. -B. ZANARDO, ERNEST SANTI. 

